Wide-gap filler material

ABSTRACT

This invention relates to a composition for repairing metallic articles which in its initial state is in the form of an adhesive, self-supporting putty, capable of being molded including 5-15% by weight of a sacrificial binder containing at least one acrylic resin and volatile solvent. The invention also relates to a kit for the composition and methods for repair.

FIELD OF THE INVENTION

[0001] This invention relates to the brazing or sintering of particulatematerials and, more specifically, to the materials used for wide-gapjoining, repair or surface coating of gas turbine components.

BACKGROUND OF THE INVENTION

[0002] Gas turbine components, such as superalloy blades and vanes, aresubjected to high temperatures and stresses during engine operation.Under such conditions they will often become physically damaged due tothe formation of cracks, voids and worn surfaces; When the damageextends beyond certain allowable limits, a decision must be made toeither repair or replace the components. Because they are expensive tomanufacture, there is considerable economic incentive to attempt repairof turbine components by methods such as welding, brazing or wide-gapbrazing.

[0003] Wide-gap brazing refers to the repair of defects too large to befilled or bridged by standard bring techniques wherein the gap fillermaterial is drawn into defects by capillary forces alone. Therefore,wide-gap filler materials must to be physically pre-placed within jointsor defects or onto surfaces and, during heat treatment, exhibit sluggishflow which prevents them from substantially flowing out of the repairarea. Prior art wide-gap filler compositions are typically comprised ofa mixture of superalloy and braze alloy powders suspended in some typeof temporary organic vehicle so as to form a slurry, paste or transfertape. The organic vehicle, or binder, is usually comprised of an organicpolymer dissolved in a solvent, and sometimes includes a plasticizer anddispersant. The organic polymer provides strength to the alloy powderdeposit after the solvent has evaporated, bonding the powder particlesto each other, as well as to the substrate article. (The word “binder”is usually used to mean all of the ingredients present in the vehicle.including the organic polymer, solvent, plasticizer, wetting agent, etc.However. in many references, the word “binder” refers specifically tothe organic polymer constituent of the vehicle. When used herein. theword “binder” shall be used in the traditional sense and the phrase“principle binder resin” shall be used to refer to the organic polymercomponent.) Subsequent drying and furnace heat treatment operationsdecompose and vaporize the various binder constituents, followed bybrazing or sintering of the powder. Alloy powders used for wide-gapfiller materials are described in U.S. Pat. Nos. 4,073,639 and4,381,944. Organic binders and methods used in the formulation ofslurries, pastes and transfer tapes have been described in U.S. Pat.Nos. 2,908,072; 3,293,072 and 3,589,952.

[0004] Historically, wide-gap repairs were developed for the repair ofdefects in aero or aero-derivative gas turbine components. Relativelyspeaking, these components and the defects in them tend to be small. Forexample, a typical wide-gap crack in an aero gas turbine component mightbe about ¼ inch in length by about 0.030 inches in width or depth. Incontrast, heavy frame gas turbines which are designed primarily forindustrial power generation are much larger than aero or aeroderivativegas turbines. A single vane segment or blade from one of these enginescan weigh upwards of 100 lbs. Crack defects in these components arecorrespondingly much larger, with dimensions often exceeding severalinches in length and up to one inch in width or depth. Standard weldingtechniques cannot always be used to successfully repair this type ofdamage, and it is again desirable to be able to use some type ofwide-gap repair process for component restoration.

[0005] While the wide-gap slurries, pastes and transfer tapes of theprior art have been found useful for the repair or joining of thesmaller areo components, there are many situations in which thesematerials are unsatisfactory for the repair of larger defects in heavyframe gas turbine components. For instance, it is often desirable to beable to apply the wide-gap filler material to thicknesses of ⅛ inch ormore onto surfaces with vertical or inverted orientations. After it isapplied, the filler material should neither flow, shrink, nor formdefects such as voids, tears and the like during subsequent handling andheat treatments. Prior art wide-gap repair materials will either slumpor fall off the article during drying and/or heat treatment when used inthis way, making it necessary to complete the brazing or liquid phasesintering operation in a number of steps by varying the orientation ofthe article in the furnace each time.

[0006] Some additional requirements of a good wide-gap filler materialare that, during its initial application, it should be capable ofplastic flow together with adhesive properties which are similar tothose of a modeiling clay. These properties would aIlow the alloy powdermanure to flow into a desired shape by appiying a moderate force, forexample by hand, and thereafter keep its shape, while adhering to thesubstrate article in various orientations. Once the external force isremoved from the wide-gap filler, it should keep its shape while therepair article is handled, stored, dried, and heat treated. Theseattributes are not found in the wide-gap slurries, pastes and transfertapes of the prior art. For example, a powder metallurgy repairmaterial, comprised of a mixture of iron-base alloy powders and aplastic binder, has been described in connection with the repair ofcentrifugal pump impellers (Welding Journal, April 1971, pp. 255-256).The proprietary materials used in this method were molded by hand,however, back-up supports were needed on the underside of through-goingdefects to hold the powder mix in place. In other words, the mixture wasnot self-supporting.

[0007] Still another limitation of prior art wide-gap filler materialshas been encountered in the repair of hollow gas turbine componentswhich contain through-going defects or details. In most cases,drop-through or flow of the repair filler material into interior coolingpassages or cavities cannot be tolerated, since obstruction of thesepassages would render the component unserviceable and unrepairable dueto the limited access afforded by the component design. It is verydifficult to control the flow of prior art wide-gap pastes and slurrieswhich makes them unsuited to the repair of these types of defects ordetails. An important advantage of the wide-gap filler material of thepresent invention is that the aforementioned limitations related tomolding, flow, slumping and loss of adhesion can be eliminated. Thisadvantage is realized through the use of the novel sacrificial bindersystem of the present invention.

[0008] Finally, within the general category of materials comprised ofmetal powder alloys and organic binders there exists another class ofmaterials which are used in the powder injection molding art. Powderinjection molding (herein. referred to as PIM) is a method for thefabrication of ceramic or metallic sintered parts. A solid green body orcompact comprised of a ceramic or metallic particulate material and asacrificial binder mixture is molded in a die by the application of heatand mechanical pressure in an injection molding machine. The binderingredients are later removed from the green body in a series of solventor thermal debinding processes, followed by firing and sintering of thecompact. The main PIM binder types are thermoplastic, thermosetting andgelation systems R. M. German. Powder Injection Molding, Metal Powderindustries Federation. Princeton, N. J., 1990, pp. 99-124).Thermoplastic sacrificial binders used in the formulation of PIMfeedstock are rigid and non-adhesive at room temperature and must besoftened by heating before the mixture will flow adequately to allowmold filling. Thermosetting and water-based gelation binders developtheir strength by cross-linking of the polymer units at elevatedtemperatures. Rigid, self-supporting compacts can only be produced fromthese materials by heating the die cavity after the feedstock has beenintroduced. The need for substantial temperature and pressure variationsduring the processing of PIM feedstocks makes the binders used in theseformulations unsuitable for use in conjunction with the wide-gap fillermaterials of the present invention.

SUMMARY OF THE INVENTION

[0009] One object of the present invention is to provide an improvedwide-gap filler material, useful for the manufacturing, joining orrepair of metallic articles which will allow the positioning and heattreatment of thick (e.g. ⅛ inch), complex, near-net-shape powder alloydeposits in horizontal, vertical or inverted orientations without theneed for surrounding back-up dams or support materials.

[0010] Another object is to provide a wide-gap filler material which, inits initial form, will remain soft, moldable, self-supporting andadhesive (tacky), even after being exposed to air at room temperatureover a period of several hours.

[0011] Still another object is to provide a wide-gap filler materialwhich will not slump, shrink, crack or flow away from its initialposition during subsequent handling or vacuum heat treatment operations,even when it is positioned in vertical or inverted orientations.

[0012] A further object is to provide a wide-gap filler material whichcan be used to fill through-going defects in hollow components wherethere is limited or no access to the interior cavity. The improvedwide-gap filler material of the present invention will not slump or dropthrough into the interior cavities of the component during applicationor processing.

[0013] These and other objects and advantages will be more fullyunderstood from the following detailed description of the preferredembodiments, which are intended to be typical of, rather than in any waylimiting on, the scope of the present invention.

[0014] Briefly, in one form of the present invention there is providedan improved sacrificial binder mixture consisting essentially of, byweight, 31-33% acrylic resin, having a glass transition temperature(T_(g)) less than 20° C., 22-24% phthalate or adipate-type plasticizer,42-44% glycol ether or glycol ether acetate with a vapor pressure ofless than 20 mm Hg. at 25° C. and 1-2% nonyl phenol base or octyl phenolbase nonionic surfactant as a wetting agent. The binder mixture iscombined with a finely divided alloy powder or blend of powders to givea composition consisting of, by weight, 5-8% of the binder mixture and92-95% of the alloy powder or powders. The resulting filler material isin the form of an adhesive, self-supporting, moldable putty, capable ofbeing forced under manually applied pressure to bond with, and take theshape of, a joint or repair cavity in any orientation.

[0015] In another form of the present invention. there is provided atwo-part (Part A and Part B) wide-gap filler material comprised of twopowdered alloys, provided as separate components, each in the form of amoldable, adhesive putty. The first component (Part A) putty comprises ametal alloy powder having as its basis metal an element selected fromthe group consisting of nickel, cobalt or iron. The first componentputty may, in addition, contain a certain amount of a non-metallic (e.g.oxide, nitride or carbide) particulate material. The second metallicalloy powder has a liquidus temperature lower than the solidustemperature of the first component particulate material(s) and thesubstrate article. The ratio of these two putty components, Part A(containing the first alloy powder(s) plus binder mixture): Part B(containing the second alloy powder plus binder mixture), is controlledto be in the range from 4:1 to 1:1, depending on the properties requiredin the final repair deposit and the processing characteristics of thealloy powders when they are used to repair or join the metal articles.

[0016] The invention in still another form provides a method for usingthe putty containing the improved sacrificial binder of the presentinvention to manufacture or repair a metallic article. After preparationand cleaning of the bonding or mating surfaces, a single or two-partalloy putty is applied to the article and shaped or molded to produce anear-net-shape build-up. The sacrificial binder ingredients are thenremoved in a controlled thermal process to prevent flow, slumping, orseparation of the repair deposits from the article. The sacrificialbinder ingredients are additionally removed by methods which allowvapors and gaseous decomposition products to escape from the wide-gapfiller material without causing internal pressure build-ups which couldotherwise lead to the formation of defects such as voids, blisters,cracks, tears and the like.

[0017] This application also relates to a kit for the composition andmethod for repair.

DESCRIPTION OF A PREFERRED EMBODIMENT

[0018] In the repair or joining of metallic articles using wide-gapfiller materials in accordance with the present invention, defectswithin worn articles are first removed by mechanical means or thesurfaces of the joint are brought into position with one another. Aparticulate filler alloy is blended with a sacrificial binder to formthe wide-gap filler and is then placed within the repair cavity orbetween the joint surfaces. Portions of the sacrificial binder areremoved by drying the article in air at temperatures up to 200° C. andthen the article is placed into a vacuum furnace to be brazed or liquidphase sintered. During the overall brazing or liquid phase sinteringprocess, the article is first held at an intermediate temperature whichcauses the reminder of the sacrificial binder ingredients to decomposeinto gaseous products and be removed by evaporation. The temperature isthen raised to a point at which the wide-gap material melts,re-solidifies and fuses with the parent metal of the article forming asound, high strength joint.

[0019] The sacrificial binder system of the present invention comprisesat least a principle binder resin which is a thermoplastic and has asoftening or glass transition temperature (T_(g)) below about 20° C.,and a solvent with a low vapor pressure, preferably less than about 20mm Hg. at 25 C. Additionally, the sacrificial binder system of thepresent invention may contain a plasticiser and a wetting agent. The lowglass transition temperature of the principle binder resin makes it softand malleable at room temperature, while the low vaporization rate ofthe solvent contributes to wet tack, adhesion and a useful working life.When combined with alloy powders, these binder properties result in awide-gap filler material with a consistency somewhat like modelling clayor adhesive putty.

[0020] The principle binder resin preferably comprises an acrylicpolymer or blend of acrylic polymers which provide a balance of cohesivestrength or rigidity and softness or flexibility. For example. a tough,hard resin which has good strength and a high softening temperature canbe plasticized with a softer. more flexible resin to give the desiredproperties. If the glass transition temperature of the principle binderresin is low enough, it may even have a slight tacky feel even beforesolvents and plasticizers are added. Acrylic resins have-other desirableproperties which make them useful as ingredients in the sacrificialbinder system of the present invention. For example, acrylic resinsremain stable above their softening range at temperatures up to 170-230°C. This property allows the selective removal of the solvent portion ofthe binder to take place by evaporation in air at temperatures up to150° C., prior to vacuum furnace heat treatment. At higher temperatures(i.e. above 260° C.), acrylics depolymerize to volatile monomers,leaving negligible ash or solid residue in the repair deposits. Someexamples of acrylic resins which are used in conjunction with thepresent invention are methacrylate, methyl methacrylate, ethylmethacrylate, n-butyl methacrylate, isobutyl methacrylate,methyl/n-butyl methacrylate, n-butyl/isobutyl methacrylate,methyl/laurel methacrylate polymers and copolymers. It is preferred thatthe principle binder resin make up 25-50% by weight of the sacrificialbinder system and most preferably 30-40% of the sacrificial bindersystem.

[0021] The solvent used in conjunction with the sacrificial binder ofthe present invention must is be active, which s to say that it iscapable of dissolving the principle binder resin. Initially the solventcontributes to the wet tackiness, softness, and moldability of thesacrificial binder system. After the wide-gap filler material has beenapplied to an article to be repaired or joined. the principle binderresin is dried and hardened by evaporation of the solvent. Thus, thesolvent must have a low volatility at room temperature in order toprovide a useful working life (e.g. several hours) once it is exposed tothe atmosphere, but substantially vaporize when heated to temperaturesup to 200° C. When used in conjunction with the sacrificial binder ofthe present invention, it is desirable that the solvent have a vaporpressure below 20 mm Hg. at ambient temperature and most preferable thatthe vapor pressure be below 1 mm Hg. at ambient temperature. The solventmust vaporize completely and cleanly during air drying and vacuumfurnace burn-out. Additionally, it is desirable that the solvent pose alow health risk during handling and drying. Solvents which arecompatible with the sacrificial binder system of the present inventionare esters such as isoamyl acetate and isobutyl acetate, hydrocarbons.such as VM&P naptha and mineral spirits and glycol ethers and acetatessuch as propylene glycol methyl ether, dipropylene glycol methyl ether,tripropylene glycol methyl ether, propylene giycol methyl ether acetateand dipropylene glycol methyl ether-acetate. The glycol ethers andacetates and hydrocarbons are most preferred in the present inventionsince they pose the lowest health risks and meet the most preferredvolatility criteria listed above. It is preferred that the solvent makeup 25-60% by weight and most preferably 30-45% of the sacrificial bindersystem.

[0022] In addition to the principle binder resin and solvent, thesacrificial binder system of the present invention may optionallycontain a plasticizer. The plasticizer further lowers the softeningtemperature of the principle binder resin and provides addedflexibility, softness and adhesion. The plasticizer must be chemicallycompatible (i.e. form solutions) with the principle binder resin andsolvent, sufficiently volatile to allow its removal during the vacuumfurnace binder burn-out process, but not sufficiently volatile to besubstantially removed during mixing, storage, molding or air drying. Theplasticizer must further completely decompose into gaseous, volatilespecies at high temperatures without leaving substantial level of solidresidue. Plasticizers which have been found to be useful in the presentinvention and which have the above desirable properties include plthalicand adipic esters. Some examples of phthalic esters which can be used toplasticize the acrylic principle binder resins are aikyl benzylphthaiate, butyl benzyl phthaiate. butyl octyl phthalate, dibutylphthalate, dicyclohexyl phthalate, diethylphthalate, dihexyl phthalate,diisodecyl phthalate. di-2-methoxyethyl phthalate, dimethyl phthalate,ditridecyl phthalate, di-2-ethylhexyl phthalate, diisooctyl and mixedoctyl phthalate, n-octyl n-decyl phthalate and isooctyl isodecylphthalate. Some examples of adipic esters which can be used toplasticize acrylic resins are dioctyl adipate. diisodecyl adipate,di-2-ethylhexyl adipate. octyl decyl adipate, diisobutyl adipate anddiisooctvl adipate. It is preferred that the plasticizer make up 0-30%by weight and most preferably 15-25% of the sacrificial binder system.

[0023] Finally, the sacrificial binder resin of the present inventionmay, optionally, contain a wetting agent. The wetting agent lowers thesurface tension of the binder system, promoting adhesion to the repaircavity or joint surfaces and dispersion of powder particles. The wettingagent must also be compatible with the other binder ingredients and burnout cleanly from the filler material leaving negligible ash or soliddeposits. Wetting agents which have been found to be useful inconjunction with the binder system of the present invention are nonyl oroctyl phenol base nonionic surfactants. Some examples of nonyt phenolbased surfactants are nonylphenol polyethylene glycol ether andnonylphenoxypolyethoxyethanol noniomic surfactant. An example of anoctyl phenol base surfactant is octylphenoxypolyethoxyethanol nonionicsurfactant. It is preferred that the wetting agent make up 0-5% byweight of the sacrificial binder system and most preferably 1-2% of thesacrificial binder system.

[0024] The metallic particulate filler alloy used in conjunction withthe sacrificial binder of the present invention can be of anycomposition or blend of powders which may be required to producesatisfactory repair joints, as required by the application. Spherical orat least regularly-shaped particles are preferred since they formsmoother, more uniform putty mixtures. Irregular or agglomerated powderparticles require larger amounts of binder and do not form smooth,homogeneous mixtures. In a preferred form of the present-invention, theparticulate material will pass through a −325 mesh standard sieve.Particles which are substantially coarser than −325 mesh size result inputty mixtures which have a granular texture and do not flow as smoothlyto fill repair cavities. A fine particle size also promotes sinteringand solid-state bonding of the filler powder to adjacent surfaces duringremoval of the last binder components in the vacuum furnace.

[0025] In preparing the moldable, self-supporting wide-gap fillermaterials of the present invention, it is essential that the ratio ofthe sacrificial binder to the particulate alloy be controlled to producethe desired properties. If too little of the sacrificial binder is used,the repair filler material will have a granular texture, lackingsufficient cohesive and adhesive strength to be properly shaped andmolded. If an excess of binder is used, a number of problems may beencountered including slumping of the repair deposit during handling,drying or heat treatment due to particle settling and migration,distortion during binder removal and sintering, separation of the binderfrom the particulate constituent, leading to nonhomogeneities in theapplied filler material. The most preferred sacrificial binder/powdercomposition of the present invention corresponds to that in which thereis just enough binder present to fill the interstitial spaces betweenthe alloy powder particles. At this composition, which is known as thecritical loading point, the alloy powder particles are in an optimalpacking arrangement which results in point-to-point contact betweenadjacent particles. This is also the composition at which the puttyattains the highest viscosity and resistance to flow or deformation. Thecritical loading composition thus attains the greatest gravitational anddimensional stability, thereby preventing shrinkage and slumping of thefiller material after it is applied. The critical loading compositioncan be estimated using theoretical models which are based on thecharacteristics of the particulate material, but can also be identifiedusing simple tests derived from paint technology. Essentially, thesacrificial binder is added incrementally to the particulate materialand mixed by hand until the mixture looses its granular texture and canbe spatulated into a stiff, but coherent paste.

[0026] The preferred ratio of the sacrificial binder to particulatematerial in conjunction with the moldable wide-gap filler material ofthe present invention therefore corresponds to that of the criticalloading composition. Expressed in terms of weight percentages, thecritical loading composition typically corresponds to 5 to 8% of thebinder of the present invention. Finally, it is noted that the optimalor preferred loading compositions of prior art brazing slurries, pastesor feedstocks used for powder injection molding are substantiallydifferent than the critical loading composition. The optimalcompositions for these latter materials correspond to the case wherebinder loading exceeds the critical level in order to allow the powderparticles to settle and compact, as in the case of a slurry, extrudethrough a syringe, as in the case of a brazing paste, or flow into adie, as in the case of powder injection molding.

[0027] In preparing the wide-gap filler materials of the presentinvention, it has been found to be. particularly advantageous to premixand dissolve the sacrificial binder ingredients, followed by theaddition and mixing of the particulate alloy. Premixing the binderingredients results in rapid and complete dissolution of the principlebinder resin, solvent, plasticizer and wetting agent. The latter processcan be accomplished using a high speed (4,000 to 10,000 rpm) impellermixer. Mixing and dispersion of the particulate material with thesacrificial binder is preferably accomplished at slower speeds (25-70rpm) in a vacuum shear mixer. Vacuum mixing is considered to beessential to prevent the entrapment of air within the filler materialwhich could lead to voids in the finished repair deposits.

[0028] After the sacrificial binder and powder have been thoroughlymixed and vacuum degassed, the resulting moldable wide-gap filler puttyis ready to be discharged, packaged or used directly for repair orjoining purposes. Due to the high viscosity of the putty it will notflow freely and must be removed from the mixing container either byscraping with a spatula or by pump. Since manual scraping or scooping islaborious, time consuming and presents the risk of re-introducing airpockets into the mixture, the preferred method of removing or dischargigthe putty from the mixer is by mechanical pump. For such highly viscousmaterials, a ram/follower plate discharge system is required. In thisprocess a flat plate is forced downwards into the vessel containing themixed putty compound using a hydraulic press. The putty flows outthrough an opening in top of the follower plate, from which it may bedirectly dispensed into holding containers or packages until needed forproduction purposes. Alternatively, the putty being discharged from thefollower plate can be directed to a transfer pump and/or a pistonmetering system in those cases where repeatable, controlled amounts ofthe material are to be used, or where a controlled ratio of ingredientsis required for a specific purpose. When the material is to be appliedin variable quantities, as would be typical of the case where the repairof service-exposed gas turbine components is to be accomplished, it ispreferred that the putty be provided on flat sheets or trays. Transferpumps and metering systems are more suited to higher volume, productionline assembly or fabrication operations.

[0029] In a preferred embodiment of the present invention, the moldablewide-gap filler material is provided in the form of a two-componentcompound, supplied and packaged as a kit with dual beads of putty in aholding tray, or dispensed directly from a dual barrel cartridge. Thefirst component (Part A) has a composition substantially equivalent tothat of the basis alloy of the article to be repaired or joined, whilethe second component (Part B) has a liquidus temperature below themelting range of the first component. Alternatively, the first alloy mayhave a composition different from the basis alloy of the article to berepaired in order to provide specific engineering qualities (i.e.strength, wear or abrasion resistance). This two-component material isintended for use in conjunction with the wide-gap powder metallurgyrepair method of U.S. Pat. No. 5,156,321. In this process, Part A of thewide-gap filler material is positioned within the repair area or jointand Part B is applied onto the surface of the Part A putty, followed byheating of the article to remove the sacrificial binder and to effectpartial solid state sintering and liquid phase sintering of theparticulate material. The volume ratio of the Part A and B components isadvantageously controlled by simultaneously dispensing side-by-sidebeads of the first and second component putties from a dual dischargecartridge with a fixed discharge ratio. If they are not to be usedimmediately, the dual beads may be stored in a temporary holding tray.During application of the repair material, this fixed ratio of A to B ismaintained by using equal lengths of the two putty beads. This methodeliminates the need to weigh or measure the volume of each repairdeposit as it is being applied to the component.

[0030] The moldable wide-gap filler material of the present inventioncan be manually applied to irregular or complex-shapes using hand toolsor simply by applying finger pressure and working the putty into arepair cavity or joint. Care is taken to eliminate any voids or areas ofnon-contact between the filler and the joint surfaces which could leadto defects in the article after thermal processing. The surface of thewide-gap filler material is molded into a desirable near-net-shape whichsubstantially corresponds to the original surface contours of thearticle, thereby reducing the amount of time required to blend andfinish the surface of the joint after heat treatment.

[0031] After it is applied, the wide-gap filler material is dried in anair oven in order to remove the solvent component of the sacrificialbinder. This process ultimately hardens the filler deposit and rendersit porous so that the remainder of the binder system can be removed in asubsequent vacuum heat treatment operation without causing internalpressure build-up or defect formation due to entrapped vapors. Whenraising the temperature of the article in an air drying oven. it iscritical that the, rate of heating and solvent removal be controlled toavoid distortion, slumping or. the formation of gas porosity within theputty deposit. An exemplary drying cycle of the present inventioninvolves raising the temperature of the air drying oven to 75° C. at arate of 5 to 10° C. per minute. After holding at this temperature forfour hours, the temperature is raised at the same rate to 150° C. andheld for another four hours.

[0032] Once the filler deposits have been dried, the remainder of thesacrificial binder ingredients are removed by thermal decomposition andvaporization in a vacuum brazing or sintering furnace. Completevaporization and elimination of the last binder ingredients of thepresent invention usually occurs at temperatures below 500° C. Afterthis exposure. all solid organic residues are substantially eliminatedfrom the repair joint, leaving only the metallic alloy powder materialswhich are then melted and fused or sintered by further increases intemperature.

[0033] The binder of the present invention may also be used as anadhesive for the placement and bonding of powder alloy tapes. In manyrepair or manufacturing applications, it is a requirement that thesetapes be applied in vertical and inverted orientations. The braze pastebinders of the prior art have been used for this purpose but arm notcapable of holding thick tape deposits in these orientations. The binderof the present invention can be applied by brushing or spray to thebonding surface of the tape or substrate article and used as aneffective glue to overcome these. prior limitations.

[0034] In another embodiment, the particulate component of the wide-gapfiller material of the present invention may be a blend of alloy powderscomprised of a mixture of metallic powder and hard particles useful forcreating hard, wear or abrasion resistant layers. The hard particles maybe metal nitrides, oxides, carbides, borides, or mixtures thereof. Suchwear and abrasion resistant layers (hardfacing) can be applied to thesurface of cold-working or hot-working tools to extend their lifetimesin service. There are many applications for this type of hard coating inthe gas turbine field, on areas such as airfoil shroud faces, fuelnozzles, seal surfaces and the like.

[0035] The following examples are illustrative of the invention.

EXAMPLE 1

[0036] The combination of sacrifical binder ingredients shown in Table Iwere mixed together using a high speed impeller mixer for 5 minutes at5000 rpm. A filler alloy powder was then added to the binder ingredientsand mixed for an additional 10 minutes at 2500 rpm. The mixture was thentransferred to shallow trays where the most volatile solvents (tolueneand methyl ethyl ketone) were allowed to evaporate for 48 hours. TABLE I% WGT Methacrylate Polymer 2.70 (T_(g) = 5° C., supplied as 40% solidsin toluene) Ethyl Methacrylate Copolymer 1.05 (T_(g) = 40° C., suppliedas 30% solids in methyl ethyl ketone) Butyl Benzyl Phthalate 1.02Dipropylene Glycol Methyl Ether Acetate 2.16Octylphenoxypolyethoxyethanol Nonionic 0.07 Surfactant Repair FillerAlloy Powder (−325 mesh) 93.00

[0037] The resulting filler compound was in the form of a moldable,adhesive and self-supporting putty. This material was bonded to cleanmetal articles in vertical and inverted orientations without visiblyslumping or separating after periods of up to 24 hours at roomtemperature.

EXAMPLE 2

[0038] The sacrificial binder ingredients shown in Table II were mixedtogether using a high speed impeller mixer for 5 minutes. The filleralloy powder is then added to the binder ingredients and the resultingcombination is mixed and vacuum degassed in a double planetary mixer at1 Torr absolute pressure for an additional 10 minutes. TABLE II % WGTn-Butyl Methacrylate Polymer (T_(g) = 15° C.) 2.18 Butyl BenzylPhthalate 1.56 Dipropylene Glycol Methyl Ether Acetate 2.92Octylphenoxypolyethoxyethanol Nonionic Surfactant 0.14 Filler AlloyPowder (−325 mesh) 93.2

[0039] The resulting wide-gap putty had properties similar to thosedescribed above f6r the putty mixture of Example 1.

EXAMPLE 3

[0040] During an engine overhaul, a cobalt-based industrial gas turbinevane segment, with a composition as given in Table III, was inspectedand found to contain numerous large cracks. The defects were of suchsize and location as to prevent them from being welded without the riskof creating additional cracks and distortions within the component. Thecracks were also present in various horizontal, vertical and invertedorientations. The defects were first mechanically removed by grinding,leaving surface discontinuities to be repaired. The vane segment wascleaned for four hours at 1150° C. under a partial pressure of hydrogen.A two-part repair filler material comprised of two powdered alloys wasprepared, with each part provided separately in the form of a moldable,adhesive putty. The first alloy powder (Part A) was a precipitation-strengthened nickel-base superalloy. The second alloy powder (Part B)was also a nickel-based powder with a melting range lower than the firstalloy powder, due to the addition of boron as a melting pointsuppressant. The weight percent contents of the two alloy powderconstituents are also given in Table III. Each of these two powders wasmixed separately with the sacrificial binder ingredients to give puttycompositions as defined in Table II.

[0041] Part A filler putty was manually positioned and shaped to filleach repair cavity. Part B putty was applied on top of the Part A puttydeposit. The vane segment was dried in air for four hours at 75° C. andthen for an additional four hours at 150° C. The article was transferredto a vacuum heat treating furnace which was evacuated to an absolutepressure of less than 1×10⁻⁴Torr. The temperature was initially raisedto 250° C. over a period of about 30 minutes. Over the next 3 hours, thetemperature of the furnace was raised to 450° C. while outgassing of theremaining binder ingredients occurred. Over the next 5 hours thetemperature of the furnace was raised to 1204° C. and held for 2 hourswhich resulted in liquid phase sintering of the repair filler material.The article was then cooled to room temperature to yield the finalrepaired part. The sintered repair filler material was completely.bonded to the metal article and did not show signs of shrinkage,separation or flow, even in areas where the deposits were in invertedand vertical orientations. The small amount of positive material on thesurface of the defects was then manually blended away to restore theoriginal surface contour of each repair area. TABLE III Part A Part BCobalt-Based Filler Alloy Braze Alloy Element Vane Alloy (−325 Mesh)(−325 Mesh) Ni 10.5 Balance Balance Cr 25.5 16.0 14.0 Co Balance 8.510.0 Al 3.5 3.5 Ti 3.5 W 7.5 2.6 Mo 1.75 Ta 1.75 2.5 Nb 0.85 C 0.25 0.10B 0.01 0.01 2.7 Zr 0.06 Y 0.06

EXAMPLE 4

[0042] The combination of sacrificial binder ingredients shown in TableIV are mixed together using a high speed impeller mixer for 5 minutes at5000 rpm. A filler alloy powder is then added to the binder ingredientsand mixed for an additional 10 minutes at 2500 rpm. The mixture is thentransferred to shallow trays where the most volatile solvents (tolueneand methyl ethyl ketone) are allowed to evaporate for 48 hours. TABLE IV% WGT Methacrylate Polymer 3.25 (T_(g) = 5° C., supplied as 40% solidsin toluene) Ethyl Methacrylate Copolymer 1.05 (T_(g) = 40° C., suppliedas 30% solids in methyl ethyl ketone) Dipropylene Glycol Methyl EtherAcetate 2.16 Repair Filler Alloy Powder (−325 mesh) 93.59

[0043] The resulting filler compound is in the form of a moldable,adhesive and self-supporting putty. This example demonstrates asacrificial binder composition which excludes plasticizer and wettingagent. The low glass transition temperature of the Methacrylate Polymer(which, together with the Ethyl Methacrylate Copolymer, constitutes theprinciple binder resin) provides sufficient plasticity to make amoldable putty.

EXAMPLE 5

[0044] For comparison with the wide-gap filler material of the presentinvention, two wide-gap filler compositions were prepared which werecomprised of alloy powders mixed with commercially available braze pastebinders. The two commercial binders used for this purpose are well knownand widely used by those skilled in the brazing art. They are consideredto be typical of the two general classes of braze paste binderscurrently in use: (i) water-based gel binders containing polymersderived from natural cellulose and (ii) solvent-based binders containingsynthetic organic polymers (thermoplastics). In the first comparativewide-gap filler, a nickel-based alloy powder, with a compositionequivalent to that of the Part A Filler Powder in Table III, was mixedwith a commercial braze paste binder known as “KAO” (Omni TechnologiesCorporation, Exeter,. N.H.). This binder is a water-based gel containingcellulose ether (approximately 3%) as the principle binder resin andthickener. The KAO binder was added to the alloy powder incrementally tothe point at which the mixture was no longer granular, but formed astiff, cohesive paste; the total amount of KAO being in the range of 4-6weight percent.

[0045] A second comparative wide gap filler material was prepared usingthe same alloy powder and another commercial braze paste binder known asNicrobraz 500 Cement (Wall Colmonoy Corporation, Madison Heights,Mich.). This binder is comprised of a plastic (approximately 6 weightpercent) dissolved in an organic solvent (1-1-1 Trichloroethane). Awide-gap filler putty containing this binder was prepared in the sameway as for the KAO binder, using approximately 4-6% weight percent ofthe Nicrobraz 500 Cement.

[0046] For each of these two commercial braze paste binders, it is to benoted that the amounts of the principle binder resins, cellulose etherand plastic, are much lower (3 and 6 weight percent, respectively) thanin the sacrificial binder of the present invention (25-50 weightpercent), but as stated above, they are typical of those currently usedin the art. In addition, the organic solvent used in the Nicrobraz 500cement, 1-1-1 trichloroethane, has a much higher vapour pressure(approximately 125 mm Hg. at 25° C.) than the solvents preferred for usein the sacrificial binder of the present invention.

[0047] These two comparative wide-gap filler materials were found to beinferior to the wide-gap filler material of the present invention forthe following reasons:

[0048] 1. They were both weak and did not have enough firmness or “body”to be easily molded by hand into free standing shapes. On the contrary,they each had a wet consistency and tended to pull appart easily duringhandling. It was suspected that this was due to the low levels ofprinciple binder resin and high solvent levels in each of the commercialbinders. This weakness also made each of the comparative wide-gapfillers prone to slumping and distortion during handling.

[0049] 2. The comparative wide-gap filler materials would not adhere tovertical and inverted surfaces. Once again, the low levels of principlebinder resin were thought to be responsible for the poor performance.

[0050] 3. The comparative wide-gap filler materials each dried out tooquickly. Their surfaces became hard and brittle after 10 to 15 minutesof exposure to air, making them prone to tearing and cracking whenattempts were made to mold them into free-standing shapes after thisperiod of time had elapsed. This deficiency was caused by thecomparatively high vapour pressures and fast evaporation rates of thesolvents used in the commercial braze paste binders.

EXAMPLE 6

[0051] A two-part, high-temperature hardfacing compound is formulated asfollows using the sacrificial binder ingredients of Example 2 and nickelchromium-chromium carbide composite powders whose mesh sizes are both−325 mesh. TABLE V % WGT Part A n-Butyl Methacrylate Polymer (T_(g) =15° C.) 4.91 Butyl Benzyl Phthalate 3.51 Dipropylene Glycol Methyl EtherAcetate 6.56 Octylphenoxypolyethoxyethanol Nonionic Surfactant 0.32Metco 83 VF-NS Composite Powder, −325 Mesh 84.7 (50% chromium carbideclad with 50% nickel-chromium alloy) Part B n-Butyl Methacrylate Polymer(T_(g) = 15° C.) 2.18 Butyl Benzyl Phthalate 1.56 Dipropylene GlycolMethyl Ether Acetate 2.92 Octylphenoxypolyethoxyethanol NonionicSurfactant 0.14 Amdry XPT 476 Alloy Powder, −325 Mesh 93.2(Ni—15Cr—3.5B)

[0052] Each Part is in the form of a moldable, adhesive andself-supporting putty. The Part A putty is applied to the Z-notch(contact surface) of a shrouded industrial turbine blade. The Part Bputty is applied to the surface of the Part A putty to give anapproximate weight ratio of 60:40, Part A:Part B.

[0053] The composite powder deposits are dried in air for four hours at75° C. and then for an additional four hours at 150° C. The blade istransferred to a vacuum heat treating furnace which is evacuated to anabsolute pressure of less than 1×10⁻⁴ Torr. The temperature is initiallyraised to 250° C. over a period of about 30 minutes. Over the next 3hours, the temperature of the furnace is raised to 450° C. whileoutgassing of the remaining binder ingredients occurred. Over the next 5hours the temperature of the furnace is raised to 1176° C. and held for30 minutes which results in liquid phase sintering of the compositewide-gap filler material. The article is then cooled to room temperatureto yield the final repaired part. The bonded composite powder providesthe interlocking Z-notch contact surfaces with enhanced wear resistancewhile the blades are operating in a gas turbine engine.

[0054] The present invention has been described in connection withspecific examples and embodiments. However, it will be understood bythose skilled in the art that the invention is capable of othervariations and modifications without departing from its scope asrepresented by the appended claims. The above references are herebyincorporated by reference.

1-34. (Canceled)
 35. A binder composition consisting essentially of byweight: a) 25-50% thermoplastic resin with a glass transitiontemperature below 20° C.; b) 25-60% solvent for the thermoplastic resinwhich substantially vaporizes up to 200° C.; c) 0-30% plasticizer; andd) 0-5% wetting agent.
 36. A method for brazing or liquid-phasesintering comprising: 1) drying a metallic or alloy substrate with acomposition comprising by weight: a) 85-90% of a metal or alloy powder;b) 5-15% of binder consisting essentially of: 1) 25-50% by weight of athermoplastic resin with a glass transition temperature below 20° C.; 2)25-60% by weight of a solvent for the thermoplastic resin whichsubstantially vaporizes up to 200° C.; 3) 0-30% by weight of aplasticizer; and 4) 0-5% by weight of a wetting agent; in air attemperatures up to 200° C.; 2) maintaining said substrate at anintermediate temperature to decompose remaining binder into gaseousproducts; 3) evaporating the gaseous products; 4) heating the substrateto melt the metal or alloy powder; 5) re-solidifying the metal or alloypowder and fusing that powder to the substrate; 6) controlling rate ofheating and solvent removal to substantially avoid distortion of,slumping of or porosity in the composition.
 37. A method for repairingor joining of metallic or alloy articles comprising: mechanicallycleaning the repair or joint area to remove oxides and defects, applyingto the repair or joint area a composition comprising by weight: a)85-90% of a metal or alloy powder; b) 5-15% of binder consistingessentially of: 1) 25-50% by weight of a thermoplastic resin with aglass transition temperature below 20° C.; 2) 25-60% by weight of asolvent for the thermoplastic resin which substantially vaporizes up to200° C.; 3) 0-30% by weight of a plasticizer; and 4) 0-5% by weight of awetting agent; drying the repair or joint area with the composition inair at temperatures up to 200° C.; maintaining said area at anintermediate temperature to decompose remaining binder into gaseousproducts; evaporating the gaseous products; heating said area to meltthe metal or alloy powder; resolidifying the metal or alloy powder andfusing that powder to said area; controlling rate of heating and solventremoval to substantially avoid distortion of, slumping of or porosity inthe composition.